Bittersweet News For Neural Stem Cell Grafts

Using human embryonic stem - HES - cells directed to a neural fate to treat Parkinson's disease might be more complicated than previously thought, according to an article to be published in the November 2006 issue of Nature Medicine. The study reports that when transplanted into rats, these cells demonstrate the potential to give rise to tumors.

Parkinson's disease involves the degeneration of dopamine-releasing cells in a region of the brain known as the substantia nigra, leading to motor problems. Previous studies have attempted to coax stem cells into becoming dopamine-releasing, in the hope that they could be transplanted into the brain of people with the disease to replace the degenerated cells. One problem that researchers have encountered is the difficulty of obtaining enough cells to perform transplantation experiments in animal models.

In the current study, Steven Goldman and colleagues cultured HES cells while exposed to particular proteins and in the presence of human fetal glial, or brain 'support', cells. This allowed them to obtain enough cells to transplant into and alleviate the motor deficits of rats. However, after some time, the grafts started to show areas that no longer consisted of dopamine-releasing neurons, but of dividing cells that had the potential to give rise to tumors.

The authors believe that their findings mandate caution before moving the application of such stem cell-derived grafts to the clinic as a possible treatment for Parkinson's disease.